Laminated sheet material



Patented June 3, 1952 UNITED STATES PATENT OFFICE LAMINATED sneer MATERIAL George G. Rumberger and Alfred M. Heald,

Neenah, Wis., assignors to Marathon Corporation, Rothschild, Wis

consin a corporation of Wis- No Drawing. Application September 19, 1949, a Serial N0. 116,617

or intercalated between two or more layers of 'paraflin and microcrystalline waxes alone or-in combination with wax compatible materials that modify the properties'of the wax coating or add other functional properties to the sheet material. For example, paraifin wax coatings have been impi'oved by-the addition of rubber or polyisobutylene. Such coatings are heatsealing, flexible, stretchable,etc. Microcrystalline wax which has been used widely for laminating simply because of its adhesiveness, has been modified with ester gum, rosin esters, polyethylene, polyisobutylene, etc

The art has continuously searched for modifiers or additivesv to improve the adhesive and flexing properties of wax films, particularly at low temperature. This latter requirement has become increasingly important with the growth of the frozen food industry. Paper and paper board laminated with microcrystalline wax will delaminate at temperatures of F. to 50 F., depending on the wax used. Wax additives have been found which improve the adhesion to some degree, but these are usually high cost materials and require special blending. Flexibility has been obtained by adding plasticizers to wax, such as oil, but this has been at the sacrifice of seal strength. Though low temperature adhesion is particularly desirable in laminated sheets, it is also desirable in wax base coated sheets, particularly where the sheet is heatsealed. Frozen food carton overwraps are examples of sheets which must remain sealed at low temperature.

It is an object of this invention to provide a 13 Claims. (Cl. 154-50) ,sheet material having a wax film, or wax-base film, either as a coating or as a laminant, which has improved adhesion to the sheet material, and still a further object is to provide a film of improved flexibility, film strength, and seal strength particularly at low temperatures. It is a further object of this invention to provide laminated sheet materials which will not delaminate at temperatures as low as 5 F. It is another object to provide heatsealable coated sheets having high seal strength at such temperatures. Other objects and advantages will be apparent from the following description of our invention.

Sheet materials of our invention havea film of a hydrocarbon wax which is substantially nonreactive with urea. The-hydrocarbon wax is a novel wax of the type disclosed in a copending application of inventor, Rumberger Serial No. 110,892, filed August 1'7, 1949. Generally this wax is obtained by reacting a paraflin or microcrystalline petroleum wax with urea in the presence of a urea solvent to form a urea-wax complex with any of the reactive components of the starting wax. The urea-wax complex is separated from the nonreactive wax, as by filtration, thus a novel wax results which is substantially nonreactive with urea. This novel wax can be applied to sheet materials by conventional hot melt coating or waxing methods. These waxes are generally believed to comprise branched chain parafiins and cyclic compounds, and are substantially free from straight chain parafiins.

Laminated sheets of cellophane (regenerated cellulose) of our invention will not delaminate at temperatures as low as 5 F. or even below 0 F. in some cases. They are flexible at these temperatures hence do not crack. Cellophane laminated sheets using a wax or wax base laminant have never been available heretofore which would not delaminate and crack at such low temperatures. The poor adhesion ofwaxes to impervious sheets such as cellophane, foil, sheet metal and the like, has always presented a problem which is overcome by our sheet materials.

The wax films in our sheet materials provide as good a moisture and moisture-vapor barrier as previously known films, and further provide as good a barrier in a flexed sheet as in a fiat sheet. With prior sheet materials, because of the brittleness of the wax film this was never the case, particularly at low temperatures. Since sheet materials of our invention find their greatest use as container walls, either in the form of sealed wrappers, bags, cartons, cans etc. where the sheets are bent and formed, this improved' property is very important. v

The following specific examples will illustrate the superior properties of sheet materials of our invention.

EXAMPLE 1 I Various microcrystalline waxes manufactured by the indicated companies were treated with urea and water. In each case the urea-wax ratio was about 3 parts urea to 1 part wax which was sufllcient to remove all of the reaction wax. The amount of water used was about 2% based on the weight of the'urea. The wax was first reacted urea.- The nonreactive wax (N-wax) filtrate was heated to drive oil? any water and then was ready for coating.

Two sheets of moisture prootcellophane were laminated with about lbs. per ream (24 x 36- reactive material improves the original wax. there may be instances where only a partial removal 01' the higher melting parafilns "with urea will produce an improved wax film as a coating or laminant.

In this regard we have found that sheet materials having wax films wherein N-wax is an additive have unique and unexpected properties. Many sheet materials are coated with parafiin wax having no components melting above 150 e. g., bread wrappers, and wax wrapping papers. We have found that a minor portion of N-wax added to the parafiln wax will not only improve such a sheet as to flexibility and heatsealing strength, but will also increase the blocking temperature.

EXAMPLEZ A 25# basis weight sulfite base sheet was coated with 4# per ream oi parailln wax modified with 10% of the N-wax from Bareco 170/175 used in Example 1 which was de-oiled which N-wax has a melting point of 155 F. De-oiling was carried out by orystallizing out and separating any wax from an ethylene dichloride solution, 1 part wax to 10 parts dichloride, at 0 F. The crystallization wasrepeated. The coatedsheets were tested for blocking temperature and seal strength and 500 sheets) 0! each type of N-wax by ho melt P- the results compared to a straight paramn coated ;plication, as well as eachtype of wax. sheet. I v v 1 TABLE I Flexibility and seal strength of was: laminated cellophane F] i sealstrengtl-llr tr Description oi Yield M. P. me a Laminant percent F. l g

95F. 73F. F. 01

Quaker State Micro: a i' Regular 145 13 5'20 750 800 N-wax 130 -2 309 565 689 1, 219

Bareco Oil 00.:

170/75 Regular 171 75 10 -wax so 142 -2 285 e05 910. 14 ran s5 Regular--. 180 84 N-wax 50 15s 5 628 430 200 190/95Regular 189 97 0 N-wa so 110 15 112 131 43 Socony-Vacuum Mag- I nowax: 1

Regular 160 29 440 159 865 150 N-wax 36- 14a 1 35s 126 890 115 In the table the values for flexibility were obtained by flexing a wax strip 0.03" thick at decreasing temperatures and noting the tempera- I ture at which the strip cracked. Melting points were determined by A. S. T. M. method D8742.

Seal strength is the force in gms. required to sep-'- arate a laminated sheet 1" wide at the temperature indicated.

From Table I it is readily apparent that in.

both low temperature flexibility and seal strength, and hence are superior to sheets made from the waxes having components reactive with urea. Even Magnowax which contains only about 14% of material which is reactive with urea showed a marked improvement in flexibility after removal of this material.

The N-waxes used in Example 1 were prepared by treating the original wax with an excess of urea. These N-waxes are therefore characterized by the fact that they are substantially free from normal parafiins naturally occurring in microcrystalline wax some of which would melt above 150 F. Since, however, removal 01. any

TABLE II Seal Blocking Strength Description of Coating Temp 0F. gilxlllgfi 1;?

Paraifin .Q 90-95 80 -100 Paraffin plus N-wax 110-115 170200 Where special conditions demand properties 7 not present in our sheet materials when using N-wax alone it can be modified with conventional vwax modifiers. For example, the melting point of the laminant may be raised by adding high molecular weight polyisobutylene, rubber, polyethylene, butyl rubber, and the like. In order to take maximum advantage of the improved flexibility of our N-wax laminated sheet we prefer to add branched chain polyethylene or polyisobutylene. with these branched chain modifiers we can get flexibility in our sheet materials at temperatures below 5 F. and yet have a laminant gill not flow at temperatures as high as Particularly desirable applications for our sheet materials are 'wax coated cartons which are subject to refrigeration. Paper milk bottles for example are generally heavily coated with wax to prevent leakage. The heavy coating tends to break or flake off under refrigeration causing wax flakes to fall into the milk. Bottles made of our sheet material, that is sheets coated with N-wax,

or even a parafiln wax modified with N-wax. would obviate this problem because of the-improved cohesion and adhesion of the coating as evidenced by seal strength. Another use of N- wax or such modified parafiln wax is in making frozen food cartons. So-called "tin cans are lined with wax for certain applications, e. g., beer cans. Here again the low temperature properties of our coatings are very desirable. The improved coated sheet of Example 2 is excellent as a bread wrapper because of the high blocking temperature together with improved sealstrength.

Many other variations ,and modifications in our sheet material will be obvious to those skilled in the art and no limitations are intended by the above examples and illustrations except such as are contained in the following claims.

We claim:

1. A sheet material comprising a base sheet and a superficial film of wax on said base sheet which wax film is substantially nonreactive with urea.

2. A sheet material comprising a base sheet and a superficial film of a wax, said wax film consisting of a wax substantially free from normal parafiins.

3. A laminated sheet material comprising at least two base sheets and a film of wax intercalated therebetween which wax is substantially nonreactive with urea.

4. A container wall comprising at least two sheets of material adhered together by afilm of wax intercalated therebetween, which wax is substantially free from normal paraflins.

5. An improved sheet material for milk bottles comprising a paperboard having a superficial film of wax thereon which wax is substantially nonreactive with urea.

6. A laminated sheet material comprising at least two sheets of regenerated cellulose adhered together by a film of wax substantially free from normal parafiins.

7. A coated sheet material comprising a base sheet and a superficial film of a wax compris- 7 ing paraffin wax to which has been added a minor portion of a wax substantially free from normal 8. A container wall comprising a base sheet having superficial wax film thereon, said wax film comprising a homogeneous wax which is substantially free from normal paraflin.

9. A sheet material comprising a base sheet having superficial wax film thereon, said wax film comprising a homogeneous wax which is substantially free from normal parafiin.

10. A sheet material comprising a base sheet and a superficial film of a wax, said wax film comprising a microcrystalline wax substantially free from normal parafilns.

11. A coated sheet material comprising a base sheet and a superficial film of a wax comprising paraffin wax having no componentsmelting in excess of 150 F. to which has been added a minor portion of a de-oiled microcrystalline wax substantially free from normal parafiins.

12. A sheet material comprising a base sheet and a superficial film of wax, said wax film comprising amixture of normal and iso-paraffinic wax components wherein the highest melting of said components is iso-paramnic.

13. A coated sheet material comprising a. base sheet and a superficial film of substantially oilfree paramn wax having no components melting in excess of 150 F. to which has been added a minor portion of a microcrystalline wax substantially free from normal parafllns.

GEORGE G. RUMBERGER. ALFRED M. HEALD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Reel 143 T. O. M. (Technical Oil Mission) Film,

pages 135-139, May 22, 1946. Available for photostating at the Library of Congress only. 

3. A LAMINATED SHEET MATERIAL COMPRISING AT LEAST TWO BASE SHEETS AND A FILM OF WAX INTERCALATED THEREBETWEEN WHICH WAX IS SUBSTANTIALLY NONREACTIVE WITH UREA. 